Field of the Invention
The present invention relates to a method of polishing a back surface of a substrate, such as a wafer. The present invention also relates to a substrate processing apparatus for polishing the back surface of the substrate.
Description of the Related Art
In recent years, various types of devices, such as memory circuits, logic circuits, and image sensors (e.g., complimentary metal-oxide-semiconductor (CMOS) sensors), become more highly integrated. In processes of fabricating these devices, foreign matters, such as fine particles and dust, may be attached to the devices. The foreign matters attached to the devices may cause a defect, such as a short circuit between interconnects or a malfunction of a circuit. Therefore, in order to increase a reliability of the devices, it is necessary to clean a wafer on which the devices are formed so as to remove the foreign matters from the wafer.
The aforementioned foreign matters, such as fine particles and dust, may also be attached to a back surface of the wafer (i.e., a bare silicon surface). If such foreign matters are attached to the back surface of the wafer, the wafer may be separated from a stage reference surface of an exposure apparatus, or a front surface of the wafer may be inclined with respect to the stage reference surface, resulting in a patterning shift or a focal length error. In order to prevent such problems, it is necessary to remove the foreign matters from the back surface of the wafer.
It has been a conventional technique to scrub the wafer with a pen-type brush or a roll sponge while rotating the wafer. However, in such a conventional cleaning technique, a removal rate of the foreign matters is low. In particular, it is difficult to remove the foreign matters on which a film is deposited. Furthermore, it is difficult for the conventional cleaning technique to remove the foreign matters from the entire back surface of the wafer.